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aqa a-level physics > Chapter 12 - Electric current > Flashcards

Chapter 12 - Electric current Flashcards

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1
Q

What is the electric current?
- give equation and units

A

Rate of flow of charge
I = Q/t
units - amperes (amps) - A

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2
Q

What is an insulator?

A

Each electron attached to an atom and can’t move away from the atom. When a voltage is applied across an insulator, no current passes through because no electrons can move through the insulator.

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3
Q

What is a conductor?

A

In a metallic conductor most electrons are attached to atoms but some are delocalised - these are the charge carriers in the metal. When voltage is applied across metal the charge carriers are attracted towards the positive terminal.

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4
Q

What is a semiconductor?

A

Number of charge carriers increases with an increase in temperature. Resistance of a semiconductor decreases as temperature is raised. A pure semiconducting material is referred to as an intrinsic semiconductor.

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5
Q

What is potential difference?
- Give equation and units

A

Work done/energy transfer per unit charge.
V = W/Q
units - volts

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6
Q

What is the equation for electrical power?
- give units

A

P = IV or P = I^2R = V^2/R

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7
Q

What component is this?

A

Diode

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8
Q

What component is this?

A

Variable resistor

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9
Q

What component is this?

A

Thermistor

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10
Q

What is resistance?
- give equation and units

A

Measure of difficulty of making current pass through the component.

Resistance = PD across the component/ current through it
R = V/I
units - Ohms

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11
Q

What is resistance caused by?

A

Repeated collisions between charge carriers in the material with each other and with the fixed positive ions of the material.

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12
Q

What do we assume voltmeters and Ammeters as experiments? What does this mean?

A

That they’re ideal

  • Voltmeters assumed to have infinite resistance (no current flows through them)
  • Ammeters assumed to have no resistance (no resistance across them)
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13
Q

What is Ohm’s law?

A

Ohm’s law states that the pd across a metallic conductor is proportional to current through it, provided the physical conditions don’t change.

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14
Q

What are conductors that obey Ohm’s law called?

A

Ohmic conductors

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15
Q

What are conductors that don’t obey Ohms’s law called?

A

Non-ohmic conductors

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16
Q

Describe IV graph for an ohmic conductor?

A

Current directly proportional to potential difference, so graph is straight line as resistance doesn’t change

17
Q

Describe IV graph for a filament lamp

A

Current increases proportionally with V at low V. Increase in current causes increase in temperature (causing particles in metal to vibrate more so makes it harder for charge to flow) which increases resistance, so current decreases again. Graph levels off at high currents (rate of increase of I with V decreases)

18
Q

Describe IV graph for semiconductor diode.

A

Current only flows in one direction and requires voltage of 0.6 V in the forward direction before they will conduct.

19
Q

What is resistivity?
- give equation and units

A

Measure of difficulty of current flowing through a material.
Resistance of 1m length with a 1m^2 cross sectional area. Measured in Ohm-metres

resistivity = resistance x cross sectional area/ length

20
Q

Draw circuit used in the resistivity practical

A
21
Q

What is superconductivity?

A

When a wire or device has zero resistance below the critical temperature of the material

Resistance decreases with temperature/cooling

22
Q

What are some applications of a supercondutor?

A
  • Making high power electromagnets.
    in devices such as MRI scanners, particle accelerators and lightweight electric motors and power cables that transfer electrical energy.
23
Q

What is the meaning of ‘Negative Temperature Coefficient’?

A

Thermistor that’s resistance decreases as temperature goes up.
- Warming thermistor gives more electrons enough energy to escape from their atoms - so more charge carriers available.

24
Q

Describe resistance-temperature graph of thermistor?

A

A temperature increases the resistance decreases at a decreasing rate until it reaches a constant at a temperature.

25
Q

What applications do thermistors have?

A

Temperature sensor
- in ovens, fridges etc

26
Q

How can 2 lamps have different power ratings but have the same light intenity output?

A

In lamps energy is wasted as heat/thermal energy

So in one lamp more energy is wasted or less energy is converted to light/luminosity

27
Q

Draw a circuit you could use to measure variation of current with pd for a component/ resistance?

A

a. ) using a potential divider to vary the pd from zero
b. ) a variable resistor to vary the current to a minimum

28
Q

Draw a I-V characteristic graph for a semiconductor diode in both forward and reverse bias

A

aqa a-level physics (31 decks)

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